1. Field of the Invention
The present invention relates to an electrostatic capacitive touch pad used, for example, as a pointing device of a personal computer, and more specifically, to a touch pad which is capable of ensuring flexibility, and stabilizing a connection with a ground electrode on a product and a potential of a shield layer.
2. Description of the Related Art
The conventional touch pad has a film substrate made of an insulating synthetic resin sheet such as PET (polyethyleneterephthalate) serving as a detection substrate. On one side of the film substrate, an extension portion protruding to one side is formed. On the film substrate, an X electrode layer and a Y electrode layer are formed as two types of wiring patterns, thereby detecting an electrostatic capacity.
In more detail, an X electrode layer is formed on a bottom surface of the film substrate. The X electrode layer has an X direction driving electrode in which a plurality of X electrodes is formed with a predetermined spacing in an X direction. Further, one end of each X electrode is formed to extend to the extension portion. Moreover, a dummy electrode is formed between each pair of adjacent X electrodes.
Further, on a surface on which the X direction driving electrode of the film substrate is formed, a ground electrode is formed to extend to the extension portion along the circumferential portion of the film substrate. Moreover, between the X direction driving electrode and the ground electrode, an X switching electrode comprising a plurality of electrodes is formed.
On a surface of each electrode, an insulating film formed by coating or printing an insulating resin is provided, and a plurality of through holes is formed in the insulating film.
On a surface of the insulating film, a Y electrode layer, in which, in a direction perpendicular to the X direction driving electrode, a plurality of Y electrodes is formed and a Y direction driving electrode is formed, is arranged. Further, one end of some of the Y electrodes is formed to extend to a position of a predetermined through hole from both sides of an X direction.
Further, on the same layer as that on which the Y direction driving electrode of the insulating film is formed, a detection electrode is formed. The detection electrode comprises two comb-shaped electrodes, and each of which has a tip formed in a reverse direction to each other. Further, each comb-shaped electrode is collected to one electrode in a center of Y direction and extends to a predetermined position of a through hole.
In addition, on the entire surface that includes the Y direction driving electrode, an insulating film made of the same material as that of the insulating film is formed. Further, to a top surface of the film substrate, a surface sheet is attached by an adhesive.
An end of each Y electrode formed in the Y electrode layer is connected to the X switching electrode through a predetermined through hole formed in the insulating film.
Further, an end portion formed to extend from the detection electrode which is formed in the Y electrode layer is connected to the X switching electrode through a predetermined through hole.
In addition, an end portion of each connected electrode is formed to extend to an end portion of the extension portion of the film substrate in the Y electrode layer.
Then, an end portion of each electrode formed to extend to the end portion of the extension portion of the film substrate is connected to a conductive portion of a control circuit substrate (for example, see Japanese Unexamined Patent Application Publication No. 2003-99185 (see pages 3 to 5 and FIGS. 1 to 4)).
In the touch pad formed in such a manner, an aluminum sheet is attached to the bottom surface of the film substrate, that is, a rear surface, and the touch pad is arranged to be connected to a ground electrode such as a keyboard of a PC (personal computer).
In addition, in the touch pad connected to the keyboard, by touching the surface sheet with a conductor such as a finger, an electrostatic capacity between each X electrode and each Y electrode is varied at the touched location, and X coordinate data and Y coordinate data are detected. Then, the detected output is amplified through an amplifier and is converted into a digital signal by an A/D converter. Further, a control unit performs a predetermined calculation, and then a control is conducted in a device such as a PC.
However, the conventional touch pad is likely to generate a connection failure, then causes the potential of the shield layer to be unstable, thereby adversely affecting the operation performance of the touch pad, since the shielding aluminum sheet was attached to the rear surface of the resultant touch pad and the aluminum sheet was connected to the ground electrode of the keyboard or the like, when it is arranged in the keyboard or the like of a PC. In addition, there was a problem in that the aluminum sheet is attached to the rear surface of the touch pad and then the flexibility of the touch pad is impaired.